If Caesar Barber dreamed of winning fame, he probably didn't think it would be due to his obesity. Doubtless he had something more heroic in mind. But, since the 120kg (19-stone), 56-year-old maintenance worker from the Bronx, in New York, filed a lawsuit against McDonald's, Wendy's, Kentucky Fried Chicken and Burger King last month - seeking damages for selling him food that made him obese - Barber's 15 minutes are proving as painful as the two heart attacks he has had.

"Does anyone really believe that Mr Barber was too dumb to know that gorging himself on saturated fat was less healthy than ordering, say, a fruit dish or a chef salad?" snapped Steve Dasbach, executive director of the Libertarian Party, when Barber outed himself as a junk-food junkie.

Actually, Barber contends he was in the dark about the nutritional content, or lack thereof, of the fast food he was eating up to five times a week from the 50s onwards. Incredibly, he didn't even stop gobbling burgers and salty fries after his first heart attack in 1996.

In his lawsuit - the first of its kind in the US - he contends that deceptive advertising misled him about the nutritional value of the food, until a doctor pointed it out.

"Those people in the advertisements don't tell you what's in the food," he said. "It's all fat, fat and more fat. Now I'm obese. The fast-food industry has wrecked my life. They said 100% beef. I thought that meant it was good for you."

For days after Barber's public lament, attacks on his character and IQ became a sport in the media. Barber wasn't clueless, columnists and radio hosts shrieked, just out to make a quick buck by failing to take responsibility for his diet. Americans love fast food - a staggering 75 million people eat it every day - but who, they asked, doesn't know that too much will turn you into a Teletubby?

But Barber, a diabetic with high blood pressure, is convinced the chains hooked and then hospitalised him. "Mr Barber honestly didn't know what the dangers were when he got hooked on fast food in the 50s," says his lawyer, Samuel Hirsch.

"The fast-food chains made no effort then, and little today, to inform consumers about the dangerously high fat, cholesterol or salt content of their food. Nobody is saying that Mr Barber doesn't accept some responsibility for his situation, but it is comparative."

Hirsch says Barber was shocked by the ferocity of the attacks against him, (he is in hiding) but he himself was not. "Unlike the tobacco companies, who are viewed as malevolent groups who lied to Congress, people love the fast-food chains. McDonald's is an icon in America. We are attacking a beloved icon."

He is also at pains to point out that Barber's goal is not money - Hirsch has told him that the case is a legal minefield and he may only get medical costs - but to get the chains to inform customers that their food is guilty of expanding their waistlines.

"The public have not been educated to the dangers of fast food, they think it's economical to have it. We want the chains to disclose the calorie, fat and sodium content of all their products. We want warning labels on certain foods for people with existing health problems."

In the US, pre-packaged foods in supermarkets must carry nutrition labelling. Restaurant food need not, although a number of chains, including those Barber is suing, agreed to post or provide nutritional information after pressure from consumer groups. But many, says Hirsch, flout the agreement or display information in dark corners. "Or they produce them in difficult to understand language. You need to be a rocket scientist to read those charts."

Hirsch's legal strategy will be similar to that used by anti-tobacco lawyers in the 90s, who argued successfully that cigarette makers willfully withheld information from consumers that smoking posed a serious health risk.

Specifically, Barber's lawsuit says that fast-food restaurants negligently and recklessly engage in the sale of food that is high in fat, salt, sugar and cholesterol content, which studies show cause obesity, diabetes, coronary heart disease, high bloodpressure, strokes, raised cholesterol intake and related cancers.

But unlike cigarettes, where levels of nicotine were found to be spiked by tobacco companies to hook smokers, Steven Anderson, president of the Restaurant Owners' Association and no fan of Barber's lawsuit, argues that chains do not spike their food to keep you coming back. You do that, he says, of your own free will.

"To say his obesity is just due to the fast-food chains is twisted logic. Being overweight is a function of genetics, exercise and diet. Mr Barber should have exercised common sense. What's next, putting warning labels on the sofa and the remote control so that we don't watch too much TV?"

But not everyone in the US thinks Barber's case is a joke. The Physicians Committee for Responsible Medicine rushed to applaud the lawsuit. The committee's research coordinator, Brie Turner-McGrivey, says, whether Barber wins or loses, the hype surrounding the case has been a windfall for doctors, spotlighting America's obesity epidemic and the role fast food plays in it.

Today, one in four American adults is obese, almost double the rate in 1980. According to the American Obesity Association, obesity is characterised as a body mass index of 30 or higher. The association claims that the condition, which is often a precursor to diabetes and cardiac failure, causes about 300,000 deaths a year, costing $117m (£76m) a year in healthcare costs. "What this case highlights is that even if you think choosing fish in a fast-food restaurant is a healthy choice, it isn't," says Turner-McGrivey. "At McDonald's, a 'fillet of fish' contains 26g of fat. (The daily requirement is 65g). I think women would be surprised to learn that some of the supersize hamburgers contain the equivalent of an entire day of their calories."

While Turner-McGrivey admits fast food isn't addictive in the same way as cigarettes, she claims the high levels of sodium, sugar and fat make it so palatable consumers get hooked. Which is why, she says, Barber is right to demand labelling. "Labelling would limit people ordering larger servings. Once they saw how much fat was present, they would order the small fries instead of the supersize. That's a good start. I think this lawsuit is going to create a conversation about obesity and the link to fast food that is long overdue. The debate will also probe the way the chains market heavily to children, because getting them young sets up a lifetime of bad eating habits."

Speaking of children, Hirsch is to file another lawsuit in the coming months in which three obese children sue the fast-food chains for ruining their health."The argument that people are responsible for their actions is a bit harder to make with children," says Hirsch. "Yes, parents are responsible for them, but children are exploited through aggressive advertising and toy promotions. At a certain age, they start to go by themselves. These restaurants market themselves as benevolent friends of the kids, when the bottom line is really profit."

But Steven Anderson of the National Restaurant Association says public awareness about balanced eating - due to government schemes and a culture obsessed with being thin - has never been higher, and anyone suggesting that McDonald's has duped them into having a heart attack has to be joking.

"For Mr Barber to blame his health problems solely on the restaurant industry is really a stretch. Nobody held a gun to his head, and fast-food chains do provide alternatives like veggie burgers and salads."